China rejected yesterday calls from the United States and European businesses to join a pact eliminating import duties in the chemical sector as part of a global trade deal.

The refusal, voiced by China's ambassador to the World Trade Organization, Sun Zhenyu, showed how difficult it would be to reach agreement in one of the most sensitive areas of the WTO's long-running Doha round.

"We can't participate in the chemical sector," Mr. Sun told a panel discussion at the WTO's annual public forum.

"According to the mandate, sectors are voluntary. In this case, China is not so voluntary to join that one."

G20 leaders reaffirmed last week their goal of concluding the Doha round, now in its eighth year, in 2010.

But the United States has said the current deal does not create enough new opportunities for business.

It wants big emerging countries such as China, India and Brazil to open their markets more. A favoured option is through deals eliminating or almost eliminating tariffs in individual industrial sectors beyond any overall tariff cuts agreed in a broader agreement.

But China and other big emerging countries are suspicious of efforts to force them to join sector deals, which are voluntary under the terms of the Doha negotiations.

Mr. Sun linked China's reluctance to cut tariffs further than it has already offered, or participate in sector deals, to trade measures it faces from its partners, such as this month's increase in U.S. tariffs on Chinese tires to block imports.

"Currently, it would be very difficult for us to try to persuade our stakeholders, our industries back at home, to accept this sector at this stage," he said, citing anti-dumping and safeguard measures imposed on Chinese goods.

"That would be very difficult for us to explain."

Mr. Sun said China had already cut its chemical tariffs to 1.5%, 5% and 6.5% in many cases and these were no longer a barrier.

Rainer Quick, vice-chairman of the WTO working group of BusinessEurope, an EU industry lobby, said developing countries would not be expected to eliminate tariffs immediately but would have a transition period of several years before going to zero.

Mr. Sun said rich countries were refusing to take part in proposed sector deals that were of interest to developing countries, such as textiles, forestry, fisheries and electronics.